Though Elsa's face is never shown, her looming threat is powerful enough to get even Regina/Evil Queen (Lana Parrilla) to ready for the coming wrath. Just as the voiceover ominously hints at trouble for Storybrooke, Regina voices her dread, "Here we go again ....."

But Emma (Jennifer Morrison), in her signature red leather jacket, has her own thoughts on the new villainess: "Really?"

Comic-Con attendees in July were treated to a special first look from the premiere that featured Elsa and Anna at their parents' grave site as they prepare for Anna's wedding to Kristoff.

Executive producer Adam Horowitz told The Hollywood Reporterin May that they were "honored" to incorporate the Frozen universe into Once. "We fell in love with [the movie] when it came out last year like everyone did, and we want to do our best to do it justice," he said.